DSpace Community: KAIST Dept. of Physicshttp://hdl.handle.net/10203/524
KAIST Dept. of PhysicsThu, 12 Jul 2018 02:04:43 GMT2018-07-12T02:04:43ZPromotion of electrochemical oxygen evolution reaction by chemical coupling of cobalt to molybdenum carbidehttp://hdl.handle.net/10203/241397
Title: Promotion of electrochemical oxygen evolution reaction by chemical coupling of cobalt to molybdenum carbide
Authors: Kim, MinJoong; Kim, Sunghyun; Song, DongHoon; Oh, Se-Kwon; Chang, Kee Joo; Cho, EunAe
Abstract: Herein, we report a novel strategy to promote electrochemical oxygen evolution reaction (OER) on cobalt (Co) surface by coupling Co to molybdenum carbide (Mo2C). Chemically coupled Co and Mo2C nanoparticles were synthesized through a simple heat treatment of the mixture containing Co and Mo precursors and graphitic carbon nitride (g-C3N4). Transmission electron microscopy (TEM) images obviously showed that Co and Mo2C nanoparticles were coupled at Co/Mo2C interfaces. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculation results revealed that electrons were transferred from Co to Mo2C nanoparticles across the interfaces. The electron transfer makes the Co surface more electrophilic by d-band center of Co upshift, leading to an increase in OH- affinity. As a result, the Co nanoparticles coupled with Mo2C have OER-favorable Co-oxo and Co-hydroxo configuration within their oxidized surfaces, and hence, can accelerate the overall OER than bare Co nanoparticles. This work demonstrates that the Co nanoparticles chemically coupled to Mo2C exhibited excellent OER activity and stability in an alkaline electrolyte and suggests a promising way to design an active OER catalyst.Sun, 01 Jul 2018 00:00:00 GMThttp://hdl.handle.net/10203/2413972018-07-01T00:00:00ZTime series analysis of the Antarctic Circumpolar Wave via symbolic transfer entropyhttp://hdl.handle.net/10203/241494
Title: Time series analysis of the Antarctic Circumpolar Wave via symbolic transfer entropy
Authors: Oh, Mingi; Kim, Sehyun; Lim, Kyuseong; Kim, Soo Yong
Abstract: An attempt to interpret a large-scale climate phenomenon in the Southern Ocean (SO), the Antarctic Circumpolar Wave (ACW), has been made using an information entropy method, symbolic transfer entropy (STE). Over the areas of 50-60 degrees S latitude belt, information flow for four climate variables, sea surface temperature (SST), sea-ice edge (SIE), sea level pressure (SLP) and meridional wind speed (MWS) is examined. We found a tendency that eastward flow of information is preferred only for oceanic variables, which is a main characteristic of the ACW, an eastward wave making a circuit around the Antarctica. Since the ACW is the coherent pattern in both ocean and atmosphere it is reasonable to infer that the tendency reflects the Antarctic Circumpolar Current (ACC) encircling the Antarctica, rather than an evidence of the ACW. We observed one common feature for all four variables, a strong information flow over the area of the eastern Pacific Ocean, which suggest a signature of El Nino Southern Oscillation (ENSO). (C) 2018 Elsevier B.V. All rights reserved.Fri, 01 Jun 2018 00:00:00 GMThttp://hdl.handle.net/10203/2414942018-06-01T00:00:00ZSpin currents and spin-orbit torques in ferromagnetic trilayershttp://hdl.handle.net/10203/242526
Title: Spin currents and spin-orbit torques in ferromagnetic trilayers
Authors: Baek, Seung-heon Chris; Amin, Vivek P.; Oh, Young Wan; Go, Gyungchoon; Lee, Seung-Jae; Lee, Geun-Hee; Kim, Kab-Jin; Stiles, M. D.; Park, Byong-Guk; Lee, Kyung-Jin
Abstract: Magnetic torques generated through spin-orbit coupling(1-8) promise energy-efficient spintronic devices. For applications, it is important that these torques switch films with perpendicular magnetizations without an external magnetic field(9-14). One suggested approach(15) to enable such switching uses magnetic trilayers in which the torque on the top magnetic layer can be manipulated by changing the magnetization of the bottom layer. Spin currents generated in the bottom magnetic layer or its interfaces transit the spacer layer and exert a torque on the top magnetization. Here we demonstrate field-free switching in such structures and show that its dependence on the bottom-layer magnetization is not consistent with the anticipated bulk effects(15). We describe a mechanism for spin-current generation(16,17) at the interface between the bottom layer and the spacer layer, which gives torques that are consistent with the measured magnetization dependence. This other-layer-generated spin-orbit torque is relevant to energy-efficient control of spintronic devices.Fri, 01 Jun 2018 00:00:00 GMThttp://hdl.handle.net/10203/2425262018-06-01T00:00:00ZSubpicosecond X rotations of atomic clock stateshttp://hdl.handle.net/10203/242532
Title: Subpicosecond X rotations of atomic clock states
Authors: Song, Yunheung; Lee, Han-Gyeol; Kim, Hyosub; Jo, Hanlae; Ahn, Jaewook
Abstract: We demonstrate subpicosecond-timescale population transfer between the pair of hyperfine ground states of atomic rubidium using a single laser-pulse. Our scheme utilizes the geometric and dynamic phases induced during Rabi oscillation through the fine-structure excited state to construct an X rotation gate for the hyperfine-state qubit system. The experiment performed with a femtosecond laser and cold rubidium atoms, in a magnetooptical trap, shows over 98% maximal population transfer between the clock states.
We demonstrate subpicosecond-timescale population transfer between the pair of hyperfine ground states of atomic rubidium using a single laser-pulse. Our scheme utilizes the geometric and dynamic phases induced during Rabi oscillation through the fine-structure excited state to construct an X rotation gate for the hyperfine-state qubit system. The experiment performed with a femtosecond laser and cold rubidium atoms, in a magnetooptical trap, shows over 98% maximal population transfer between the clock states.Fri, 01 Jun 2018 00:00:00 GMThttp://hdl.handle.net/10203/2425322018-06-01T00:00:00Z